[February 05, 2014]CHAMPAIGN — When the temperature
dips below zero and the wind picks up, the wind chill becomes a
concern for anyone venturing outdoors. There are important things to
keep in mind about wind chill, according to Jim Angel, state
climatologist, at the Illinois State Water Survey, University of
Illinois.

The National Weather Service defines the wind chill as how cold
people and animals feel when outside. Wind chill is based on the
rate of heat loss from exposed skin when affected by wind and cold.

The calculations for wind chill are based on temperature and wind
speeds, usually taken at a nearby airport. While the wind speed is
adjusted for the difference between the 33-foot wind instrument and
the height of 5 feet, it is still based on winds at the airport in a
wide-open area. Areas in town with many mature trees may have
significantly lower wind speeds.

Conversely, winds between tall buildings in places like downtown
Chicago may be much higher. Therefore, the wind chill at a
particular location may be much different from that reported at the
airport.

The wind chill formula is based on bare skin of a healthy adult,
and vulnerability to frostbite or hypothermia can be higher for the
elderly and small children. On the other hand, covering bare skin
and wearing appropriate clothing greatly reduces the effects of the
cold and wind.

Sunshine is not included in the formula even though it has the
potential to moderate the effects of wind chill during the daylight
hours.

An accurate wind chill forecast requires both an accurate
temperature forecast and an accurate wind forecast. Anytime
there is a prediction of two separate weather variables, in this
case temperature and wind speed, it can be more challenging to
forecast.

"While the wind chill observations and forecasts have some
limitations, the risk of frostbite or hypothermia from severe cold,
especially if accompanied by wind, should be taken seriously," says
Angel.

The Illinois State Water Survey at the
University of Illinois at Urbana-Champaign, a division of the
Prairie Research Institute, is the primary agency in Illinois
concerned with water and atmospheric resources.